Layered semiconductors including a semiconductor layer made of GaN and formed on a base layer can be used for production of semiconductor devices such as diodes and transistors. Various studies have been conducted on producing a semiconductor device using a layered semiconductor including a semiconductor layer made of GaN. For example, PTL 1 proposes a technique in which the fraction defective during cutting into chips in the production process of semiconductor devices is reduced by controlling the defect density of a substrate, thereby improving the yield of semiconductor devices produced.